The present invention relate tetracyclododecene composition having a regulated content of compounds, which cause undesirable influences when used in various polymerizations.
Polymers and copolymers of cycloolefin have been regarded as polymers excellent in optical properties, high transparency, thermal resistance and oil-absorbency, and the cycloolefin represented by tetracyclododecene is useful as a feedstock. This cycloolefin is used for polymerization with the aid of organometallic complex catalysts, and the polymerization processes are divided roughly into two categories. In the one process, homopolymerization or copolymerization with lower xcex1-olefins at the olefin-site of said cycloolefin is carried out with Ziegler catalysts including metallocene catalysts. As the other process, metathesis polymerization with carbene-type complexes is known.
As processes for producing tetracyclododecene, the following are known. In U.S. Pat. No. 4,320,239, it is disclosed that norbornene is circulated in a process of heating xcex1-olefin, cyclopentadiene and/or dicyclopentadiene and norbornene to produce a mixture containing norbornene and tetracyclododecene.
In Japanese Laid-Open Patent Publication No. H07-173085, a composition of tetracyclododecene derivative is disclosed, which composition contains 50xcx9c5,000 ppm of the compound shown in the following formula [II], namely a trimer of cyclopentadiene. In this Publication, it is disclosed that the obtained composition of tetracyclododecene derivative can be used as a monomer for ring opening metathesis polymerization. However, no process for producing the compound is specifically disclosed. 
A product compound obtained from ethylene, cyclopentadiene and/or dicyclopentadiene and norbornene by Diels-Alder thermal addition reaction contains sometimes trimers of cyclopentadiene or the like, other than tetracyclododecene as an intended product and norbornene as an intermediate product. Because trimers of cyclopentadiene have boiling points close to that of tetracyclododecene as intended product, the formers are liable to get mixed in tetracyclododecene during distillation to obtain tetracyclododecene. As trimers of cyclopentadiene, there are a diolefin compound shown in the following formula [III] having the olefin structures both of norbornene-type and cyclopentene-type, and a diolefin compound shown in said formula [II] having two sets of norbornene-type olefin structure. In addition polymerization with a Ziegler catalyst, all of these diolefin compounds cause sometimes cross-linking reactions in homopolymerization or in copolymerization with lower xcex1-olefins at the olefin-site of cycloolefins, and further cause gelling. 
Further, when tetracyclododecene is synthesized with a feedstock comprising ethylene, cyclopentadiene and/or dicyclopentadiene and norbornene, the product contains a hydrocarbon compound having a molecular weight of 188 besides tetracyclododecene. It was found out that the presence of this compound lowers a glass transition temperature of the polymer obtained in said metathesis polymerization or the like of tetracyclododecene, while its optical properties are satisfactory. The hydrocarbon compound having a molecular weight of 188 has a boiling point so close to that of tetracyclododecene, that the former is liable to get mixed in tetracyclododecene during distillation to obtain tetracyclododecene.
Next, problems concerning the process for producing tetracyclododecene will be explained.
In Japanese Laid-Open Patent Publication No. H03-128333, a process for producing tetracyclododecene is disclosed, which comprises heating ethylene, cyclopentadiene (or dicyclopentadiene) and norbornene in the presence of an aromatic solvent. And it is mentioned that solvents such as benzene and alkylbenzene, preferably toluene, are used as aromatic solvents in order to restrain norbornene from solidifying.
According to said production process, ethylene, cyclopentadiene (or dicyclopentadiene) and norbornene are heated for reaction to obtain a mixture of norbornene and tetracyclododecene, and the produced norbornene is reused by circulating. Here, when being reused by circulating, norbornene is usually separated and recovered from a reaction mixture by distillation. However, norbornene is liable to solidify by cooling after distilled out of a distillation tower, as indicated in said Publication.
Although the recovered norbornene solidifies probably after distilled out of a distillation tower as mentioned above, the solidifying can be avoided by use of a solvent. However, when the boiling point of a solvent is exceedingly apart from that of norbornene, the concentration of the solvent in the distilled norbornene is sometimes very low. In that case, even if a solvent is used, norbornene can not be prevented from solidifying.
For example, toluene, which is especially favorable in the aromatic solvents described in said Publication has the boiling point of about 111xc2x0 C. rather different from that of norbornene of 95xc2x0 C. As a result of the difference in boiling points as mentioned above, the concentration of norbornene in a distillate containing norbornene increases (the concentration of toluene decreases), under certain conditions of distillation for recovering norbornene, and norbornene is very likely to solidify.
Furthermore, environmental problems and the influences on human body have been recently becoming the center of interest. From the viewpoint of this situation, use of aromatic compounds such as toluene has been avoided, that is, aromatic hydrocarbon solvents such as benzene, toluene and xylene are toxic to human body. For example, in the ordinance on the prevention of organic solvent poisoning, organic solvents containing more than 1 volume % of benzene are classified as the specified group-2 substance, and the dealing procedure is strictly regulated.
Processes for producing tetracyclododecene while recovering and circulating the produced norbornene are disclosed in Japanese Laid-Open Patent Publication Nos. H06-9437 and No. H06-72909 as well as said Japanese Laid-Open Patent Publication No. H03-128333. In all of these, the recovered and circulated norbornene contains dicyclopentadiene. Further, dicyclopentadiene is used as a feedstock in all of these, and commercially available dicyclopentadiene often contains methyltetrahydroindene (MTHI) as an impurity due to the fact that the starting material is a thermally cracked oil from naphtha or the like.
When MTHI contained as an impurity in commercially available dicyclopentadiene is mixed in the recovered and circulated norbornene, MTHI having the high decomposition temperature is liable to accumulate in a reaction system, and as a result, other by-products are also produced in great quantities. Though impurities other than MTHI are also contained in dicyclopentadiene, they are different from MTHI in that they decompose thermally at lower temperatures. Further, even if MTHI is decomposed by the increase of reaction temperature in a reaction system, the yield of the intended product decreases and other by-products are also produced, which both are not desirable.
In view of the circumstances as mentioned above, objects of the present invention are as follows. The one is to present tetracyclododecene compositions, which do not cause gelling due to cross-linking reaction in the case of homopolymerization or copolymerization with lower xcex1-olefins at the olefin-site of cycloolefins in addition polymerization with a Ziegler catalyst, or which do not decrease glass transition temperatures of the polymers obtained in metathesis reaction or the like. The other is to present a method for producing a tetracyclododecene composition efficiently, by preventing solidification of norbornene distilled out in the process of production and by removing impurities such as MTHI from norbornene.